1. Field of the Invention
The present invention relates to a solid-state image pickup device, and in particular, to a solid-state image pickup device in which photosensitive cells are arranged in a one-dimensional or two-dimensional array.
2. Description of the Prior Art
There has been conventionally developed an amplification-type of solid-state image pickup device which includes a phototransistor functioning as a photosensitive cell and an IGFET serving as a read circuit serially connected to the phototransistor. For example, in a solid-state pickup device disclosed in the Japanese Patent Laid-Open Publication No. 181371/1983, photocarriers generated in a base region of a phototransistor in response to light incident thereto flow into a source region of an IGFET functioning also as a collector, for example, to be stored therein. In this case, by virtue of the current amplification of the phototransistor, the electric charges resultant from multiplying the photocarriers flowing from the base to the collector by its amplification factor are stored in the source region. When the gate of IGFET is opened, the stored charges can be read in the form of a signal current associated with the photocarriers.
Such an image pickup device is characterized by functioning to amplify the readout current. However, it is necessary to include a contact forming an emitter electrode of the phototransistor, which is not suitable for manufacturing an integrated photosensitive cell array with a higher pixel density. In addition, the amplifying function is developed in response to a strong incident light in a manner similar to a weak incident light. Consequently, in an image pickup device having such an amplification characteristic, it is impossible to realize a dynamic range for implementing so-called photographic characteristics in which sensitivity is higher with a lower intensity of illumination and lower with higher intensity.